Feed-through bushing for cryogenic transformers



April 22, 1969 P. c. LAIR 3,440,326

FEED-THROUGH BUSHING FOR CRYOGENIC TRANSFORMERS Filed Deo. 6, 1967 United States Patent Oice 3,440,326 Patented Apr. 22, 1969 3,440,326 FEED-THROUGH BUSHING FOR CRYOGENIC TRANSFORMERS Philippe C. Lair, Puteaux, France, assignor to Alsthom- Savoisienne, St. Ouen, France, a corporation of France Filed Dec. 6, 1967, Ser. No. 688,470 Claims priority, application France, Dec. 8, 1966,

Inf. ci. Huib 17/26,7/34

U.S. Cl. 174--9 s 5 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a feed-through bushing for cryogenic transformers, and more particularly to transformers operating at temperatures in 'the range of from K. to 16 K., in which the cooling is obtained by a cryogenic fluid, such as liquid hydrogen, liquid nitrogen, liquid helium, liquid neon, or the like.

Feed-through bushings usually contain a central conductor surrounded by an insulating element, which is usually provided with metallic inserts to provide for equipotential surfaces, to prevent steep electrostatic gradients. An external insulator, for example of porcelain or other vitrified materials, protects the feed-through assembly.

Feed-through bushing for cryogenic transformers pose special problems because cryogenic fluids must be passed into the transformer. By making the electrical conductor for the cryogenic transformer hollow, the fluid may be passed through the conductor. The fluid must, however, be connected to external cryogenic installations and it is desirable that the external cryogenic auxiliary equipment is not subjected to elevated potentials, which may exist at the electrical terminals of the feed-through conductors. Due to the very low temperatures, icing or frosting may occur at the outside of the insulator. This is undesirable both from an electrical as well as from a maintenance point of view.

It is an object of the present invention to provide a feed-through bushing for cryogenic transformers in which cryogenic fluid can be passed through the bushing, as well as an electrical connection made, which is efficient and effective.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, in accordance with the present invention, the feed-through bushing for a cryogenic transformer includes a central hollow conductor in cylindrical form. One end of this hollow conductor extends into the cryogenie transformer, the other therebeyond. A tube is located around the conductor, spaced from the outside of the hollow cylindrical tube, the space between the tube and the hollow cylindrical conductor being evacuated. At the outside of the tube, an insulating element in the form of a thick sleeve is provided. The sleeve may have metallic cylinders inserted therein to provide for even distribution of ele-ctrical gradients. The outside of the insulating sleeve is secured to the wall of the cryogenic transformer. A reservoir is mounted at the outer end of the assembly of central conductor, surrounding tube and insulating sleeve. An outside insulator is connected at a lower end to the outside wall of the cryogenic transformer, and at its upper end to the reservoir. Space between the outer insulator and the insulating sleeve is likewise evacuated.

rfhe two, evacuated spaces thus provided form an excellent thermal insulation. The central conductor permits passage of cryogenic fluid between the interior of Ithe cryogenic transformer and the reservoir.

In. accordance with a feature of the invention, a tube made of insulating material such as, for example, Teflon, is spirally wound along the internal face of the outside insulator. The top end of the Teflon tube connects with the reservoir, the lower end being brought out from beneath the outer insulator for connection to cryogenic apparatus. Thus, only a very small potential gradient between the reservoir and cryogenic installations will arise.

In accordance with a further feature of the invention, a further insulating wall is located between the insulator sleeve and the outer insulator, tightly connected to the outer insulator at its ends, in order to form a space in which a re-heating fluid can be introduced, in order to avoid the formation of frost at the outside surface of the outer insulator.

The structure, organization, and operation of the invention will now be described more specifically with reference to the accompanying drawings, wherein:

The single figure illustrates a longitudinal, cross-sectional view of the insulator feed-through bushing, it being understood that the parts of the bushing, in plane view, would be concentric circles.

Referring now to the figure: a cyrogenic vessel has a wall formed of a pair of metal structures 1, 2. It is to be understood that the cryogenic vessel would be in the lower part, with respect to the figure, the upper part, that is above wall 2, being at outside ambient temperature. A central conductor 3 provides electrical connection to the interior of the cryogenic transformer. It can be conneted to an electrical current source, not shown. A reservoir 4, for example of stainless steel and providing a variable volume therein, is connected to the central conductor 3, which is hollow. The interior of the hollow conductor 3 is used to supply cryogenic fluid to the interior of the cryogenic transformer. Reservoir 4 is not thermally insulated with respect to the atmosphere. A heat-gradient will thus exist, progressively, in the conductor 3 within the cryogenic fluid, which will be at a higher temperature in reservoir 4 than in the interior of the cryogenic device.

A tubular wall structure 5, for example of metallized glass, stainless steel, or the like surrounds conductor 3, leaving a space 6 between the conductor 3 and Wall 5, which space 6 is closed o at the top and at the bottom, for example by welding, bonding, or other process. The space 6 is evacuated. I-t could, however, also be filled with a highly thermally insulating substance, for example a thermal insulator similar to that used in cryostats. An insulating member 7, such as a sleeve, is formed around wall 5. Stainless steel leaves, in cylindrical form, of a few microns of thickness are inserted into the insulating sleeve. They are shown at 8 on the drawings, and provide for equalization of potential gradient, as Well known in the art. The reservoir 4 is soldered, brazed, Welded, or otherwise secured to the tube 5.

The insulating sleeve 7 is tightly sealed and connected to wall 1 by a metallic collar 9, adhered to the insulating block 7, and adhered, bolted, or both adhered and bolted to the wall 1. Wall 2 is tightly sealed and connected to a exible stainless steel cylinder 10, which in turn connects to a metallic ange 11 on which, in well-known manner, by means of clamps or interlocking connections (not shown), a porcelain insulator 12 is secured. The porcelain insulator 12, at its upper end, is secured to the reservoir 4 in like manner.

A space 13 is formed between walls 1 and 2 and lille-d with a highly thermal insulation material. Space 14, between insulator 12 and the insulating sleeve 7 is highly evacuated. This evacuation may extend into space 13, at least if this space is not separately subject to a vacuum.

A11 insulating wall 15 is located parallel to the interior wall of insulator 12. Wall 15 may, for example, be laminated impregnated paper, or some laminated or vitried glass product, preferably impregnated with synthetic resin. Wall 15 is connected to the iiange 11 by means of clamps, interlocking connections and the like, as known in the art (and not shown, for simplicity, in `the drawing). The space 16 between wall 15 and the interior surface of insulator 12 may have heated mineral oil introduced thereto in order to prevent the formation of ice or frost at the outside of insulator 12. Oil may be supplied, for example, by a conduit 17 and taken off by an outlet .18.

The space 16, likewise, has enclosed therein a spiral 19 of Teflon (polytetratluoroethylene). The Teflon spiral is connected at 20 with the interior of the reservoir 4 and has an outlet from the bushing as seen at 21. Cryogenic fluid is taken out from outlet 21, somewhat heated after having been in reservoir 4, and can be conducted to cryogenic regeneration devices, not shown and well known in the art.

The vacuum in space 6 and in space 114,if provided, is obtained in the well-known manner by means of a vacuum pump, not shown. Space 6, may, after evacuation, be sealed tightly under vacuum without continuous pumping being necessary.

I claim:

1. Electrical lead-in bushing passing through the wall of a cryogenic device comprising:

a hollow central, elongated cylindrical conductor, having one end located within the cryogenic device and the other end outside thereof;

a tubular member located around the outside of said hollow, cylindrical conductor, spaced therefrom, and sealed to the ends of said conductor, the space between said tubular member and said conductor being evacuated;

an electrical insulating sleeve surrounding said tubular member;

means tightly, and in sealed relation interconnecting said insulating sleeve and the wall of said cryogenic device;

a reservoir mounted at the outside of said cryogenic device and at the end of said tubular conductor and communicating with lthe hollow interior thereof;

an outer insulator secured at its upper end to said reservoir;

connecting means tightly interconnecting the lower end of said outer insulator and the wall of the cryogenic device; p

the space between said outer insulator and said insulating sleeve being evacuated.

2. Lead-in bushing in accordance with claim 1 further comprising a spirally wound tube of insulating material located along the internal wall of said outer insulator, the upper end of said spiral tube being in liuid communication with said reservoir, and the lower end of said spiral tube leading out from said bushing.

3. Lead-in bushing as claimed in claim 2 wherein said spiral tube is made of polytetrauoroethylene.

4. Lead-in bushing in accordance with claim 1 further including an insulating wall located along the internal surface of said outer insulator, spaced therefrom, and tightly connetced thereto; fluid inlet and outlet means interconnecting the upper and lower ends of said space between the internal face of said outer insulator and said wall to provide for circulation of heating uid within said space.

5. Lead-in bushing as claimed in claim 1 wherein said means interconnecting the outer insulator and the wall of said cryogenic device includes a stainless steel flexible cylinder.

References Cited UNITED STATES PATENTS 1,856,125 5/1932 Austin. 1,897,257 2/1933 Iansson 174--9 2,099,666 1l/l937 Terpak 174-31 X FOREIGN PATENTS 227,877 4/ 1960 Australia. 1,257,157 2/1961 France.

LARAMIE E. ASKIN, Primary Examiner.

U.S. Cl. X.R. 174-15, 18, 3l 

